Leaf Age as a Determinant in Stomatal Control of Water Loss from Cotton during Water Stress

Abstract

The stomatal resistance of individual leaves of young cotton plants (Gossypium hirsutum L. var. Stoneville 213) was measured during a period of soil moisture stress under conditions of constant evaporative demand. When plants were subjected to increasing soil water stress, increases in stomatal resistance occurred first on the lower leaves and the stomata on the upper surfaces were the most sensitive to decreasing leaf-water potential. Stomatal closure proceeded from the oldest leaves to the youngest as the stress became more severe. This apparent effect of leaf age was not due to radiation differences during the stress period. Radiation adjustments on individual leaves during their development altered the stomatal closure potential for all leaves, but did not change the within-plant pattern. Our data indicate that no single value of leaf water potential will adequately represent a threshold for stomatal closure in cotton. Rather, the stomatal resistance of each leaf is uniquely related to its own water potential as modified by age and radiation regime during development. The effect of age on stress-induced stomatal closure was not associated with a loss of potassium from older leaves. Increases in both the free and bound forms of abscisic acid were observed in water-stressed plants, but the largest accumulations occurred in the youngest leaves. Thus, the pattern of abscisic acid accumulation in response to water stress did not parallel the pattern of stomatal closure induced by water stress.It is generally recognized that light intensity and leaf water potential are two of the most important factors controlling stomatal resistance of whole plants or individual leaves. The possible interaction between leaf age and stomatal response to reduced light intensity or low soil or plant water potential is frequently alluded to, but has seldom been the primary topic of research reports.Studies by Turner (25,26), Turner and Incoll (28) were reached by Gee and Federer for beech and birch leaves (7).Brown and Rosenberg (3) also demonstrated that the Rs2 of similarly illuminated sugar beet leaves was independent of age except for the most immature leaves.In contrast with the above reports, data by Slatyer and Bierhuizen (20) and Holmgren et al. (9) indicated that R8 of leaves of cotton grown under controlled conditions increased with age. The authors (20) suggested that additional leaf growth during the aging period may have been associated with solute translocation and consequent senescence of the test leaves. This same general result was obtained by Solarova (22) with primary leaves of bean. The R8 of both surfaces increased gradually with aging, but the increases were retarded when shading was eliminated or the plants were decapitated. In a recent study, Davis (5) found increases in leaf resistance of beans occurred at a nearly constant "developmental age" (80% of time from leaf maturity to death) regardless of leaf position on the plant.The above cited reports support the conclusion that reduced illumination...

Endogenous Gibberellin and Abscisic Acid Content as Related to Senescence of Detached Lettuce Leaves

“…Intact old leaves of lettuce, like other such leaves (14,15,18,19), contain the lowest level of ABA compared with younger leaves. However, old lettuce leaves seem to be the most sensitive to exogenous ABA as measured by Chl loss (unpublished results).…”

“…While it has been shown that ABA accelerates senescence in leaves, it is doubtful whether this hormone serves as a primary "senescence factor" (17,18). This doubt is strengthened by the frequent lack of correlation between ABA content and leaf age (14,15,18,19 Senescing of Leaves and Treatment with Growth Regulators. Detached leaves or harvested heads were kept in darkness in a ventilated humid chamber (100% RH, 25 C).…”

Osmoregulation in Cotton in Response to Water Stress

“…Older, fully expanded leaves had lower leaf conductances than younger leaves at the same water potentials. Jordan et al (22) demonstrated that stomatal response of cotton to leaf water potential depended uniquely on leaf age. Older adapted leaves exhibited leaf conductances somewhat higher than did nonadapted counterparts (Fig.…”

“…Turgor pressure was calculated as the difference between total leaf water potential and osmotic potential. Osmotic potentials were not corrected for the dilution of cell sap with apoplastic water that occurs during freezing (22). Leaf resistances were converted to conductances by taking the reciprocal of total leaf resistance obtained by assuming individual surface resistances act in parallel.…”

Leaf Diffusive Resistance and Water Economy in Carbon Dioxide‐enriched Rice Plants

“…However, the references cited above, although confirming the general response pattern for stomatal behaviour in COg-enriched rice plants, did not explain the ontogenetic progression because the treatments were applied only for a few days. However, seasonal changes in leaf diffusive resistance have been widely used as an indicator of stomatal responses to environmental variables and water stress in many species (Kanemasu & Tanner, 1969;Brown & Rosenberg, 1970;Gee & Federer, 1972;Turner & Begg, 1973;Jordan, Brown & Thomas, 1975;Turner & Heichel, 1977;Sandanam et al, 1981). In most of these studies, an effect of leaf age on stomatal response has been demonstrated.…”